The present invention generally relates to optical processing systems and more particularly to a wavelength-synchronized optical processing device that produces an optical signal having a wavelength that is synchronized to a stabilized wavelength of a reference optical beam and various optical information processing systems that use such an optical processing device.
With the extensive deployment of optical telecommunication networks, studies are made on the optical transmission and reception in the optical exchange systems and optical subscriber systems. Among others, there is a proposal to transmit a plurality of optical signals having different wavelengths on a common optical fiber or optical waveguide in the wavelength multiplex mode. In such a wavelength multiplex transmission of optical signals, it is necessary to superpose (i.e., multiplex) the optical signals with sufficient wavelength interval such that a reception side can demultiplex the received optical signal into individual optical signal components with reliability. In such wavelength multiplex systems, it will be easily understood that the change or fluctuation of the oscillation wavelength occurring in the optical signals causes a disastrous effect in the operation of the reception side systems.
FIG. 1 shows the block diagram of a conventional optical processing system that uses a wavelength converter 1a.
Referring to FIG. 1, the wavelength converter 1a is supplied with an input optical signal having a wavelength of .lambda..sub.0 and produces an output optical signal with a wavelength of .lambda..sub.1. There, the wavelength converter converts the wavelength of the input optical signal to a second wavelength, and the optical signal having the wavelength .lambda..sub.1 is divided out from the converted optical signal in response to a reference optical beam, supplied given externally, having the wavelength .lambda..sub.1.
More specifically, the output optical signal of the wavelength converter 1a is supplied to an optical divider 2a that divides the incident optical beam into a first output beam corresponding to the output optical signal and a second output beam, and the second output beam is supplied to a wavelength comparator 3a. The wavelength comparator 3a is further supplied with the reference optical beam and produces an electric output indicative of the difference between the wavelength of the output optical signal of the converter 1a and the wavelength .lambda..sub.1 of the reference optical beam.
The output electric signal of the comparator 3a is supplied to a controller 4a that in turn produces a control signal for controlling the operation of the wavelength converter 1a. According to this system, one can convert the wavelength .lambda..sub.0 of the incident optical signal to the wavelength .lambda..sub.1 by controlling the converter 1a such that the output of the wavelength comparator 3a becomes zero. The wavelength converter 1a may be formed by using a DFB laser diode that can change the oscillation wavelength thereof by controlling the bias current or temperature.
FIG. 2 shows another conventional wavelength conversion system wherein an input optical signal having a wavelength .lambda..sub.0 is supplied to a photoelectric converter 1b that produces an electric output in response to the incident optical signal. The output electric signal is supplied to a clock extraction circuit 2b wherein a clock signal is extracted from the information that is modulated on the input optical signal. The clock extraction circuit further discriminates the logic level of the binary information signal modulated on the input optical beam with a timing given by the clocks, and drives an optical modulator 3b. The optical modulator 3b is thereby supplied with a reference optical beam with the wavelength .lambda..sub.1 and modulates the same in accordance with the electric output of the clock extraction circuit 2b. As a result, an optical output signal is obtained with the wavelength .lambda..sub.1.
In any of these conventional optical processing systems, there has been a problem in that the normal operation of the system is not achieved when there is a fluctuation in the wavelength of the input optical beam. It should be noted that, in the telecommunication systems, there is no guarantee that the transmission side uses the stabilized optical source with respect to the oscillation wavelength. Further, such a fluctuation of the wavelength of the optical signal may be caused as a result of the dispersion of optical pulses that occur in the optical fibers. Thus, the optical transmission system is not only required to eliminate the fluctuation of the wavelength of the optical source at the transmission side but is also required to have an ability to adapt to the fluctuation of wavelength and to eliminate the same at the reception side or at any intermediate locations between the transmission side and the reception side.